#include <Eigen/Dense>
#include<iostream>
int main() {
Eigen::Matrix3d mat1, mat2;
mat1 << 1, 0, 0, 0, 1, 0, 0, 0, 1;
mat2 << 3, 0, 0, 0, 3, 0, 0, 0, 3;
std::cout << mat1 * mat2 <<std::endl;
}
